The terrorist group Islamic State (IS) has claimed responsibility for the mass shooting at a concert hall in Moscow on March 22 that has left at least 40 people dead. A post on the group’s Telegram, said: “Soldiers of the Islamic State attacked a big crowd of Christians in the city of Krasnogorsk…killing and wounding hundreds.” The post also claimed the attackers “withdrew safely” after the attack. IS has in the past claimed responsibility for attacks it did not carry out. U.S. intelligence officials, however, confirmed the claim shortly after the post. Sources told CNN’s Alex Marquardt that…